A liner is a length of tubular suspended in a wellbore, and which normally does not extend to the surface. In exemplary applications, liners are used to repair damaged casing strings, or to test questionable production zones. A liner hanger secures the liner within the well bore, and typically includes radially movably slips with teeth for biting engagement with the outer casing or sides of the "open hole" bore. The liner may be mechanically "set" in the well by axially moving the drill string with respect to the slips, thereby forcing the teeth radially outward into biting engagement with the casing.
A liner setting tool is conventionally placed on the drill string axially above the liner hanger, and assists in setting the liner hanger. Once the liner hanger has been set, the liner setting tool can be released from the liner hanger by rotating the drill string. Most importantly, the setting tool should allow for the quick yet reliable disengagement of the liner hanger, so that the setting tool and drill string can be retrieved to the surface, leaving the hanger and liner fixedly positioned in the well bore. In certain applications, e.g., when cementing a liner in place, it is preferable that the liner hanger be set and the setting tool structurally be disengaged from the liner hanger, while thereafter still employing the setting tool for rotating the drill string.
A significant problem with many prior art liner setting tools is that the liner hanger may be prematurely or inadvertently released from the setting tool during the process of positioning the equipment at its desired depth in the wellbore. A liner may, for example, be 100 feet or more in length and have a diameter only slightly less than the downhole casing through which it passes. If the wellbore is vertical and the liner diameter is substantially less than the downhole casing diameter, the entire drill string may remain in tension while lowering the equipment in place due to the weight of the drill string and liner, in which case premature release of the liner hanger may not be a problem. If, however, the well bore is highly deviated or perhaps has substantially horizontal portions, or if the liner or liner hanger gets "stuck" in a casing only slightly larger in diameter than the liner hanger, the drill string is frequently used to "push" the setting tool, liner hanger, and the liner through the well bore. In this case, axial movement of the drill string with respect to the liner hanger is possible, so that premature unlocking of the setting tool may occur. Moreover, the accidental unlocking of the setting tool may not be known to operators at the surface, who may then attempt rotate the drill string to free the presumed "hang-up". This action, in turn, may cause the inadvertent release of a liner hanger from the setting tool, thereby necessitating a more costly retrieval operation.
One type of prior art liner assembly, hereinafter referred to as the TIW RRP liner assembly, includes an elongate setting collar with an upper spline receiving section and a lower spline receiving section. The drill string above and below the setting tool includes an upper spline and a lower spline, with the connecting nut of the setting tool being axially spaced between the splines. The lower spline may be engaged to rotate the liner prior to setting of the liner hanger. The upper spline may be engaged to rotate the liner subsequent to releasing the hanger from the setting tool nut.
Engagement of one of the splines in the TIW RRP assembly would also prevent inadvertent separation of the setting tool and liner hanger while the assembly was being positioned in the wellbore. This equipment has, however, significant drawbacks over other liner hanger setting equipment. The spline arrangement and setting collar are expensive to manufacture. To rotate the liner after setting the liner hanger, the upper spline must be properly aligned to mate with the upper spline receiving section of the setting collar. If a liner is to be reset in a well,the tubing string must be carefully manipulated so that the lower and upper splines pass through their respective sections of the setting collar. The splines may become damaged or their ends deformed by the "blind" attempt to align these components, so that the desired liner rotation or resetting operation can thereafter not be successfully accomplished. Lastly, rotation of the setting tool and drill string subsequent to the setting of the liner hanger requires that the lower spline be pulled upward through the lower spline receiving section of the setting collar in order to retrieve the setting tool. Dogs on the lower spline may be spring biased to quickly pass by the lower spline receiving section, but the dogs can become locked or jammed in a fully or partially extended position. In this case, the drill string must be rotated so that the dogs are in alignment with the spline receiving portion, so that the lower spline can pass upwards for retrieval. This latter operation, which takes time and patience, conflicts wih the operator's desire to quickly retrieve the setting tool after cementing is complete to insure that the setting tool and drill string do not become stuck in a cemented wellbore.
The disadvantages of the prior art are overcome by the present invention, and an improved setting tool and method of setting a liner or other downhole tool are hereinafter disclosed.